Materials having an epitaxial crystal structure having crystal orientation, such as oxide superconductive materials and solar cell membranes, are used in various fields focusing on their specific properties. Examples of the materials are oxide superconductive materials for forming superconductive conductors, superconductive shields, and the like to be applied to various electrical appliances. Here, materials having an epitaxial crystal structure generally have poor workability and are also sometimes disadvantageous in terms of cost in the production of bulk materials. Therefore, they are normally used as a thin film formed on a predetermined substrate.
Since a substrate for forming an epitaxial film epitaxially grows crystals having a textured structure, the surface thereof also needs to have a textured structure. As such a substrate, the present inventors found a textured substrate made basically of copper (Patent Document 1). This copper substrate for growing an epitaxial film focuses on the ease of crystal orientation control of copper, and has a {100}<001> cube texture wherein the drift angle Δϕ of a crystal axis is as follows: Δϕ≤6°. In this substrate, a stainless steel or like metal layer (base material) is cladded to solve the problem of the insufficient strength of copper containing no alloying elements.
The present inventors made some modifications to the above textured substrate to improve the quality of the epitaxial film formed thereon. For example, the present inventors disclosed the above textured substrate including a copper layer, having an adequate amount of nickel thin film layer laminated on the copper surface to further improve the crystal orientation (Patent Document 2), and the like